1. Field of the Invention
The present invention relates to a wafer processing apparatus having dust proof function used in manufacturing processes for semiconductor devices, electronic parts and related products, or optical disks etc. The dust proof function is a function to prevent dust that is generated due to an opening/closing operation of an opening portion of the processing apparatus from entering the interior of the processing apparatus, when a semiconductor wafer (which will be simply referred to as wafer hereinafter) is transferred from a clean box for storing wafers into the processing apparatus through the opening portion of the processing apparatus for processing.
2. Related Background Art
Manufacturing of wafers, which are used for semiconductor devices etc., must be performed under a condition in which a high degree of cleanness is ensured. Therefore, the manufacturing of wafers was generally performed in a clean room the whole interior of which is kept in a highly clean condition. However construction and maintenance of a large clean room with a high degree of cleanness require a significant initial investment and service costs. In addition, even if once a plant investment is made for such a clean room, a modification of the layout of the room might be required later due to a modification in the manufacturing process, which would require a large additional investment. Therefore, use of clean rooms is uneconomical. In view of the above-described situation, recently a certain method has been widely adopted, that is, to keep a high degree of cleanness not within the whole interior space of a room but only within a small environmental space (which will be referred to as a mini-environment) inside a processing apparatus to attain the effects same as those obtained by keeping a high degree of cleanness within the whole of the room. (In the following, a processing apparatus that adopts this method will be called a clean apparatus.)
Specifically, in that method, clean apparatus are set in a manufacturing room with a certain layout, and wafers are transferred from one clean apparatus to another within a wafer storage container (which will be referred to as a clean box hereinafter) whose interior is kept in a highly clean condition. The clean box is attached to a predetermined opening provided on a clean apparatus in such a way as to prevent dust from entering from the exterior, and the wafers are brought into and out of the clean apparatus through that opening. Thus, the space to which the wafers are exposed can be always kept highly clean without a need for establishing a highly clean condition within the whole interior of the manufacturing room. Therefore, this method realizes the effects same as those attained by establishing a clean room condition within the whole of the room, and so it is possible to reduce construction and maintenance costs to realize an effective manufacturing process.
In the above-described clean apparatus, in order for the mini-environment to be kept in a highly clean condition, the pressure within the mini-environmental portion is arranged to a pressure (Pa+ΔP) that is higher than the external ambient pressure (represented here as Pa, which is generally the atmospheric pressure) by a predetermined pressure difference (ΔP). This creates an overall airflow from the interior of the mini-environment to the exterior thereof, so that dust would be exhausted to the exterior. In addition, airflow from the exterior can be prevented from entering the mini-environment, which prevents dust in the exterior from entering the mini-environment.
Conventionally, the general understanding has been that if the mini-environment is sealed as tight as possible, it is possible to prevent external dust from entering and to establish a high degree of cleanness. Therefore, the mini-environment is isolated from the external environment and placed in a completely sealed state by a door that closes the opening provided on the mini-environment except when the mini-environment is connected with the clean box for transferring of the wafer.
In the conventional apparatus as described above, since the mini-environment is isolated from the exterior or the ambient except for during the transfer of a wafer, the wafer in the interior is kept in a highly cleans condition. However, when the door is opened for transferring of the wafer, airflow from the interior of the mini-environment to the exterior is created due to the above-described pressure difference ΔP between the interior and the exterior of the mini-environment, which causes the following problem.
As described above, as long as an additional pressure is applied to the interior of the mini-environment, the airflow is inevitably created when the door is opened. In the conventional apparatus, the pressure difference ΔP is especially large at the moment when the door is opened. Therefore, the flow rate of the airflow created at the moment of opening the door is larger than the flow rate created by a pressure difference ΔP after elapse of a certain time. In addition, the airflow generated at the moment of opening the door involves significant turbulence.
On the other hand, the pressure in a clean box is substantially equal to the atmospheric pressure, and therefore, when airflow involving turbulence is generated at the opening, the airflow will be drawn into the interior of the clean box. The airflow flowing out of the opening generally includes dust to be exhausted from the interior of the mini-environment. In addition, dust in the exterior is also stirred up by the airflow. Therefore, the airflow drawn into the clean box includes dust, which will contaminate the wafers inside the clean box to deteriorate the quality of the wafers.